BRITTLE STARS: PRIMITIVE YET INCREDIBLY COMPLEX STARFISH
BRITTLE STARS are closely related to starfish, and in particular to Basket Stars. They are commonly known as “serpent stars”, having 5 long, thin arms that may grow as long as 2 feet long. There are lots of different types of brittle star – at least 2000 – and they are found in every ocean on earth from the poles to the tropics. In Bahamian waters they a commonly found living on reefs.
Although these creatures look primitive, their structure, nervous systems, respiratory systems, digestive systems, sex lives and transportation methods are incredibly complex. Take it from me – I’ve just read about it all. So I’ve decided to pick a few aspects of these creatures to highlight rather than discuss the minutiae of their ossicles (tiny bones), madroporites (a sort of water filter / pressure balancer) and viscera.
A DOZEN BRITTLE STAR FACTS TO PLAY WITH
- The star has no eyes and no sense organs as we know them, but can detect light chemically; and (why would they need this?) sense smell through their ‘feet’… [Not a superpower I would prize, but still]
- The mouth is on the underside of the central disc (‘body’) of 5 segments, each with a toothed jaw
- The mouth is used both for ingestion and, putting it delicately, egestion. [Nor that superpower]
- Stars eat tiny organisms suspended in the water or mini-worms, gathering them with their arms
- If I have understood this, they breathe through their armpits, and can excrete from here also
- The arms fit the main part with ball and socket joints, and are flexible in all directions
- The genitals seem to be located in or between the armpits (lucky we are not descended from stars)
- Stars readily regenerate lost arms until they lose the 5th – then they are in real trouble
- This enables them to shed an arm in a predator attack, like a lizard its tail
- Trials indicate that a jettisoned arm cannot regenerate from itself
- They use only 4 arms to move along, with the fifth ‘steering’ out in front or trailing behind
- Brittle Stars are inedible but non-toxic
I quite liked this infographic from a source new to me, ‘Weird ‘n’ Wild Creatures Wikia’
Here is a great video from Neptune Canada of a brittle star fight on the ocean floor over the remains of a shrimp. If you watch the ones joining the fight, you will clearly see the locomotion method described above, with one limb pathfinding and the other four ‘walking’.
I’m not renowned for extreme sensitivity, so I feel no shame in showing mating brittle stars, courtesy of Channel Banks. It’s not exactly Lady Chatterley and Mellors, but the entwined arms are rather romantic, no?
Credits: all wonderful photos by Melinda Riger of Grand Bahama Scuba; BS infographic and viddys as credited